Women face daily and widespread exposure to hundreds of chemicals linked to breast cancer, and reducing — or even understanding — this environmental contamination might do as much as screening or treatment to reduce a woman’s risk of getting the cancer, according to one of the most thorough reviews of the science to date.

The review, being published today in a special supplement to the journal Cancer, attempts to assess the state of the science of all riskfactors thought to contribute to breast cancer: diet, physical activity, body size and environmental pollutants.

The conclusion: Breast cancer is not just hereditary, and routine environmental exposures and lifestyle choices play a role. Reducing those routine exposures — our so-called “body burden” — has the potential to “significantly reduce the risk of cancer for many thousands of women.”

The report is authored by two advocacy groups, Texas-based Susan G. Komen for the Cure and the Massachusetts-based Silent Spring Institute.

Breast cancer is the most common invasive cancer in women worldwide and the leading cause of death in U.S. women in mid-life. Many identified risk factors — family history, age at menarche and menopause, age of first full-term pregnancy — cannot be easily avoided. That makes identifying risks that can be avoided all the more important, scientists at the Komen center wrote.

Take hormones. Researchers reported earlier this year that breast cancer incidence in 2003 dropped 7 percent, meaning 14,000 fewer women developed cancer that year than in 2002. The drop, researchers say, is likely because of reduced use of hormone replacement therapy.

Yet many synthetic chemicals — pesticides, plastic softeners, plastic additives — in everyday products act like hormones at low doses. Their effects are poorly understood, particularly when it comes to breast cancer risks. But the science is catching up.

“It’s hard to know exactly how big an effect,” said Ruthann Rudel, a senior scientist with Silent Spring. “But the evidence is becoming clearer that there is something there.”

The review found consistent evidence reinforcing the importance of physical activity and its potential to lower a woman’s risk of developing breast cancer. It also found that, while alcohol consumption increases breast cancer risk, the science on diet is too scattered to support any clear recommendations.

The biggest question mark, however, concerns environmental contaminants. Human studies simply have not provided much information about common synthetic chemicals that may be linked to breast cancer.

The review identified 216 chemicals of every stripe known to cause mammary gland tumors in animal studies. Compounds included industrial chemicals, air pollutants, radiation, pharmaceuticals, even natural products such as flavorings, Rudel said.

Some are fairly widespread, including mutagens associated with chlorine-disinfected drinking water and diesel exhaust. Yet for the most part, Rudel noted, regulators and environmental health doctors haven’t even looked for a connection between exposure and breast cancer risk in humans.

“You have to ask the question right, and if you don’t ask the question, you don’t see it,” Rudel said. “That’s been true for a long time in environmental health: You don’t always ask the right question when you start out.”

A searchable database of all 216 chemicals, including detailed information on 97 of the most widespread, is available at http://www.komen.org/environment and http://www.silentspring.org/sciencereview. The database also contains summaries and critical reviews of significant research linking breast cancer and diet, physical activity, body size, environmental pollutants and genetics.